This invention relates to a method of treating dust and sludge produced from an iron mill simultaneously with molten steel slag produced in a steel making process by mixing the dust and sludge with the slag.
In general, dust and sludge produced in the steel making process in an iron mill contain iron oxide as main component and also zinc, lead, cadmium, chromium, nickl copper, manganese, etc. as minor components. Because of the presence of the above minor components, difficulties were encountered in disposing of them as industrial wastes, which required a huge cost for the disposal.
Meanwhile, in an iron mill, a steel slag is produced in the steel making process in a converter or an electric furnace. Although studies have been made on its reuse as resources, the reuse of the whole amount of the slag produced has not been realized, and the slag has been disposed as waste, because of its swelling and crumbling properties attributable to the presence of free lime, 2CaO, SiO.sub.2 etc. in the steel slag.
Accordingly, attempts have been made to modify the steel slag which had been disposed as waste so that the swelling and crumbling of the slag can be prevented. For example, conventional methods for modification of slag include a method as disclosed in U.S. Pat. No. 4,179,279 in which a red mud (in some cases nonferrous metal slag, decomposed granite and slate) is added as a modifier in a predetermined amount to molten steel slag.
However, since no sufficient mixing of the modifiers with the slag can be attained by mere addition thereof to the slag, a bubbling gas was introduced into the molten steel slag using a lance pipe to induce convection of the molten steel slag, thereby causing a slag modifying reaction.
Therefore, the above method has drawbacks such as necessity of the use of a lance pipe for introduction of a bubbling gas into molten steel slag and an apparatus for supporting the lance pipe.
Further, the above method is disadvantageous also in that wasteful labor and equipment are required, because the lance pipe inserted into the molten steel slag is attacked in its inserted portion by the molten steel slag is attacked in its inserted portion by the molten steel slag, which requires frequent repair and replacement thereof.
In the conventional method, when the temperature of the gas introduced into the molten steel slag through a lance pipe is too low or the amount of the modifier or dust or sludge added is too large, the molten steel slag is cooled, leading to poor convection of the molten steel slag, which in turn causes an insufficient slag modifying reaction which is endothermic.